1. Field of the Invention
The present invention relates to an image forming apparatus that can perform image forming while positioned either upright or horizontally, and particularly to an image forming apparatus that in consonance with its installed attitude feeds powered developer from a developing unit to a latent image carrier.
2. Description of the Related Art
To satisfy the demand for plain paper image recording, latent image forming apparatuses, such as electrophotographic apparatuses, are employed for such image forming apparatuses as copy machines, printers, and facsimile machines. In such an image forming apparatus, electrostatic latent images are formed on a photosensitive drum, and are developed by using powdered developer to visualize the images. After the developed images are transferred to a sheet of paper, the transferred images are fixed to the sheet.
As efficient utilization of office space is one of the objects of the recent trend towards automated offices, a demand has arisen for image forming apparatuses that can be positioned either upright or horizontally. Dependent on user need and preference, such an apparatus can be installed where the available space is restricted either horizontally or vertically.
Usually, electrophotographic printers are positioned and operated horizontally, that is, with their sheet feeding paths parallel to their base planes. The arrangement of the internally mounted developing units, etc. of these printers is designed for the effective utilization of gravitational attraction. Therefore such printers function imperfectly when they are positioned and operated upright, that is, with their sheet feeding paths perpendicular to their base planes.
As examples of prior art, Japanese Unexamined Patent Publication No. Sho 58-130345 and Japanese Unexamined Utility Model Publication No. Sho 60-184061 disclose how to transport in an upright position image forming apparatuses that are operated horizontally. According to these prior art examples, spillage of powdered developer is prevented even when the apparatus is transported upright. For this purpose, a magnet is provided inside the developing unit to attract and retain the developer therein, or the developer is retained in the lower portion of the developing unit by gravity.
When such conventional image forming apparatuses are installed upright, however, the directional effect of gravity on the developing units is changed and internally stored powdered developer flows in a different direction. As a result, a developing process cannot be smoothly performed while the apparatuses are positioned upright. Since the objects of the above described prior art is to prevent developer from spilling when the apparatuses are positioned upright, this means that the flow of developer is stopped, and thus arranged apparatuses cannot perform developing processes as long as they are upright.
Another prior art example, Japanese Unexamined Patent Publication No. Hei 4-323125, discloses an image forming apparatus that forms images while it is positioned either horizontally or upright. This image forming apparatus will be explained while referring to FIG. 1. In FIG. 1A, the image forming apparatus is set up for horizontal operation; in FIG. 1B, the image forming apparatus is set up for upright operation.
As shown in FIG. 1A, a sheet of paper in a hopper 80 is extracted by a pickup roller 81 and fed to a photosensitive drum 90. Positioned around the periphery of the photosensitive drum 90 are a charger 91, an LED head 92, a developing unit 93, a transfer roller 94, and a cleaner 95. The charger 91 electrifies the photosensitive drum 90, and the LED head 92 exposes the photosensitive drum 90 to light image and forms electrostatic latent images on its surface. Thereafter, powdered developer is supplied by the developing unit 93 to develop-the electrostatic latent images on the photosensitive drum 90, and the developed images on the photosensitive drum 90 are transferred to the fed sheet by the transfer roller 94. The sheet to which the images are transferred is then fed to a fixing unit 96 to fix the developed images on the sheet. Finally, the sheet is discharged to a stacker 84 by a discharge roller pair 82 and 83. An image forming process performed by the apparatus while it is upright, as is shown in FIG. 1B, is the same as is described above.
For this prior art example, the specific processing performed by the developing unit 93 when the apparatus is positioned upright and horizontally is not described. Investigating the toner moving operation of FIGS. 1A and 1B, however, since supplemental toner is fed vertically from the upper compartment of the developing unit 93 when the apparatus is positioned horizontally as is shown in FIG. 1A, toner supplementation is enabled by gravitational attraction of the toner. But when the apparatus is in an upright position, as is shown in FIG. 1B, the feeding direction for toner is horizontal and it seemed that toner supplementation cannot be efficiently performed. Further, the developing unit 93 supplies developer to the photosensitive drum 90 in a horizontal direction, as is depicted in FIG. 1A for the horizontal installation position, but the developing unit 93 must feed the developer upward, against the force of gravity, when the apparatus is in an upright position, as is depicted in FIG. 1B. Also, the developer tends to migrate to the toner supplementation compartment and the height of the retained developer is not constant. Consequently, the developing roller feeds developer unevenly and the resulting developed images are often imperfectly formed.